When a magnetic field is applied to a conductor carrying a current, in a direction at right angles to the current, an electromotive force is produced across the conductor in a direction perpendicular to both the current and to the magnetic field. This effect, known as the Hall effect after E. H. Hall who discovered it in thin metallic foils in 1879, has become one of the most powerful tools for studying the electronic properties of semiconductors. As it is most commonly used today, the measurement of the Hall voltage enables a process engineer to determine the number of current carriers per unit volume within a semiconductor device, and also whether they are positively or negatively charged.
In the past, certain classes of semiconductor devices have utilized the Hall effect for particularized applications. For example, U.S. Pat. No. 4,516,144 discloses a magnetically sensitive semiconductor device used to sense crankshaft angle positions in automotive systems. In the operation of that device, carriers from an emitter region travel through a base region toward one or the other of a pair of spaced-apart collector regions. The carriers are deflected toward one or the other collector regions according to the polarity of a perpendicularly applied magnetic field. The strength and direction of the magnetic field is determined by the crankshaft angle position.
Despite previous attempts aimed at developing a viable semiconductor magnetic memory, the integration of a magnetic memory storage element and a semiconductor sensor device has thus far proven to be a formidable task. Applicant is unaware of the existence of any Hall effect magnetic semiconductor memory device which is feasible for use in today's very large scale integrated (VLSI) circuits and which meets the storage requirements of most modern computer systems.
The present invention combines a magnetic storage element with an integral solid-state sensor and/or amplifier to form a novel memory cell that is at once very small, static, non-volatile, and which provides high performance at a relatively low cost. As will be seen, data is stored in the form of magnetized patches or domains in a magnetic material placed in close proximity to a semiconductor sensor. In a preferred embodiment, the magnetic field is directed vertically through the semiconductor sensor to generate a transverse voltage in accordance with the Hall effect. In other implementations, multiple domains are produced within the patch to store analog data. The adaptability of the basic memory cell of the present invention is such that it lends itself to numerous embodiments and alternative methods of reading and writing information.